US4437740A - Quick return beam splitter for a single lens reflex camera - Google Patents
Quick return beam splitter for a single lens reflex camera Download PDFInfo
- Publication number
- US4437740A US4437740A US06/407,473 US40747382A US4437740A US 4437740 A US4437740 A US 4437740A US 40747382 A US40747382 A US 40747382A US 4437740 A US4437740 A US 4437740A
- Authority
- US
- United States
- Prior art keywords
- beam splitter
- reflecting film
- reflection factor
- quick return
- return beam
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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Classifications
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
- G03B19/00—Cameras
- G03B19/02—Still-picture cameras
- G03B19/12—Reflex cameras with single objective and a movable reflector or a partly-transmitting mirror
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
- G03B7/00—Control of exposure by setting shutters, diaphragms or filters, separately or conjointly
- G03B7/08—Control effected solely on the basis of the response, to the intensity of the light received by the camera, of a built-in light-sensitive device
- G03B7/099—Arrangement of photoelectric elements in or on the camera
- G03B7/0993—Arrangement of photoelectric elements in or on the camera in the camera
- G03B7/0997—Through the lens [TTL] measuring
- G03B7/09971—Through the lens [TTL] measuring in mirror-reflex cameras
- G03B7/09972—Through the lens [TTL] measuring in mirror-reflex cameras using the mirror as sensor light reflecting or transmitting member
Definitions
- This invention relates to a beam splitter disposed rearwardly of the picture-taking lens for dividing the light from the picture-taking lens.
- a beam splitter having a dielectric material multilayer film deposited by evaporation on a transparent substrate such as a glass substrate is usually used as a quick return beam splitter for a single lens reflex camera.
- This beam splitter has an advantage that since it has substantially the same reflection factor in any portion thereof, an object image relatively excellent in resolution as compared with that in a beam splitter of the type hereinafter described is formed on the focusing plate of the viewfinder optical system.
- this beam splitter has a polarizing characteristic and this has led to the possibility that a metering error arises when the light from the object is a polarized light.
- Beam splitters are also known in which non-evaporated portions in the form of spots or slits are provided on the surface of a transparent substrate and a metal film is deposited by evaporation on the portions of the surface other than the non-evaporated portions (Asahi Camera, July, 1963, P. 215, Asahi Camera, July, 1965, pl. 232, Japanese Patent Publication No. 29793/1969, U.S. Pat. No. 4,081,807 and Japanese Laid-open Patent Application No. 119030/1978).
- the portion on which a metal film is formed acts as a reflecting surface and the portion on which the metal film is not formed acts as a light-transmitting surface.
- Such beam splitters have no polarizing characteristic unlike the previously mentioned beam splitter and therefore do not give rise to the problem of metering errors resulting from polarized light.
- Such beam splitters have light-transmitting portions in the form of spots or numerous slits and this leads to the disadvantage that the resolving power is reduced. Further, in such beam splitters, if an attempt is made to increase the quantity of transmitted light, various disadvantages would arise.
- Such an object can be achieved by disposing a metal reflecting film of high reflection factor and a reflecting film of low reflection factor partly on a substrate.
- This beam splitter which uses a metal reflecting film does not suffer from the problem of polarization and, even if the reflecting film of low reflection factor is formed by an interference film, the problem of polarization is reduced as a whole. Further, in this beam splitter, the portion other than the metal reflecting film also is a reflecting film of low reflection factor and therefore, the sum of the areas of the metal reflecting film portions can be made relatively small and thus, the aforementioned problems that the pattern can be seen and that flare arises are alleviated.
- FIG. 1 is a fragmentary view showing the optical system of a single lens reflex camera to which the present invention is applied.
- FIG. 2 shows the transmission factor distribution of the complex area type quick return beam splitter according to the present invention.
- FIG. 3 shows the transmission factor distribution of the simple area type quick return beam splitter.
- FIGS. 4 and 5 show patterns on the quick return beam splitter according to the present invention.
- reference numeral 1 designates a picture-taking lens.
- a quick return mirror 2 is disposed rearwardly of the lens 1 and is positioned at its shown position when a shutter, not shown, is in its operative condition. When the shutter is operated, the quick return mirror 2 is rotated in the direction of arrow and becomes positioned outside the light beam from the lens 1.
- the mirror 2 comprises a beam splitter 3 and a beam splitter support 4.
- the beam splitter 3 has a metal reflecting film portion 5 of high reflection factor and a reflecting film portion 6 of low reflection factor formed on a transparent substrate such as glass.
- the light reflected by the metal reflecting film 5 and the reflecting film portion 6 of low reflection factor of the beam splitter 3 travels toward a focusing plate 7.
- the image of an object formed on the focusing plate 7 may be observed through a pentaprism 8 and an eyepiece 9.
- the light passed through the reflecting film portion of low reflection factor of the beam splitter 3 passes through an opening in the support 4, and thereafter is downwardly directed by a sub-mirror 10.
- Designated by 11 is a light-dividing element provided at the bottom of the camera. This light-dividing element 11 divides a light into three, and forms three images of the predetermined film surface and the surfaces before and behind the predetermined film surface on the arrays of an array sensor 12.
- Whether the picture-taking lens 1 is forming a focused image on the film surface is judged from the conditions of these images.
- the thickness of the metal reflecting film portion is 0.5 mm and the thickness of the transmitting portion is 0.5 mm, as shown in FIG. 3.
- the reflection factor of the glass surface of the transmitting portion is 0% (actually, there is a reflection of 4% in the boundary surface between the glass substrate and the air, but if the boundary surface is subjected to a transmission factor increasing treatment, there will be a reflection of the order of 0.1%).
- the beam splitter of the present invention has a small reflection factor difference as compared with the beam splitter of the prior art comprising a combination of a metal reflecting film portion and a transmitting portion, whereby the pattern of the beam splitter becomes difficult to see and the area of the metal reflecting film portion can be made smaller and thus, the aforementioned problem of flare can be reduced.
- FIGS. 4 and 5 show beam splitters which differ in pattern configuration from the beam splitter of FIG. 1.
- a feature of this pattern configuration is that the rate at which the reflecting film 6 of the low reflection factor occupies is higher in the neighborhood of the point whereat the mirror intersects the optical axis and said rate becomes lower in the direction away from the optical axis.
- the size of the reflecting film of low reflection factor along the direction corresponding to the row direction of the array sensor 12 of FIG. 1, namely, the lateral direction in FIGS. 4 and 5, is determined such that there is not formed an image having a frequency component higher than the space frequency 2PS twice the pitch of the array sensor.
- the array sensor cannot properly resolve any space frequency component higher than the Nyquist frequency defined by the space frequency 2PS twice the sensor pitch P and accordingly there occurs a hindrance to the proper reading of information and for this reason, by determining the size of this reflecting film of low reflection factor, it is caused to act as a low-pass filter.
- the film is a glass substrate-Al (600 ⁇ 1000 ⁇ )-MgF 2 ( ⁇ 1000 ⁇ )-ZrO 2 ( ⁇ 700 ⁇ )-air, and a dielectric material film renders the reflection of the Al film higher and performs the role of a protective film.
- the glass surface lacking an Al film is formed only of a dielectric material film and has a reflection factor of about 30%.
- the complex area type quick return beam splitter of the present invention is a complex area type quick return beam splitter having a reflecting film having a whole surface of 20-30% and an area type mirror and has all the excellent effects possessed by the area type quick return beam splitter and also has the excellent effect that the resolving power of the viewfinder image is enhanced to improve the quality of image and the darkening of the pattern is decreased. It has been found that the complex area type quick return beam splitter of the present invention displays an excellent function particularly when used as the quick return beam splitter of a single lens reflex camera which has a focus adjusting mechanism and requires as much light as possible in the sensor.
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Cameras In General (AREA)
- Viewfinders (AREA)
Abstract
Description
Claims (5)
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP56129168A JPS5830744A (en) | 1981-08-18 | 1981-08-18 | Quick return beam splitter for single-lens reflex camera |
JP56-29168 | 1981-08-18 |
Publications (1)
Publication Number | Publication Date |
---|---|
US4437740A true US4437740A (en) | 1984-03-20 |
Family
ID=15002815
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US06/407,473 Expired - Lifetime US4437740A (en) | 1981-08-18 | 1982-08-12 | Quick return beam splitter for a single lens reflex camera |
Country Status (2)
Country | Link |
---|---|
US (1) | US4437740A (en) |
JP (1) | JPS5830744A (en) |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4615603A (en) * | 1983-10-05 | 1986-10-07 | Canon Kabushiki Kaisha | Single lens reflex camera |
US4656517A (en) * | 1984-05-23 | 1987-04-07 | Dainippon Screen Mfg. Co., Ltd. | Method for increasing resolution of array sensor and system therefor |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP3127195B2 (en) * | 1994-12-06 | 2001-01-22 | シャープ株式会社 | Light emitting device and method of manufacturing the same |
-
1981
- 1981-08-18 JP JP56129168A patent/JPS5830744A/en active Pending
-
1982
- 1982-08-12 US US06/407,473 patent/US4437740A/en not_active Expired - Lifetime
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4615603A (en) * | 1983-10-05 | 1986-10-07 | Canon Kabushiki Kaisha | Single lens reflex camera |
US4656517A (en) * | 1984-05-23 | 1987-04-07 | Dainippon Screen Mfg. Co., Ltd. | Method for increasing resolution of array sensor and system therefor |
Also Published As
Publication number | Publication date |
---|---|
JPS5830744A (en) | 1983-02-23 |
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AS | Assignment |
Owner name: CAON KABUSHIKI KAISHA 30-2 3-CHOME,SHIMOMARUKO,OHT Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNORS:SUZUKI, TAKASHI;ITO, SUSUMU;REEL/FRAME:004034/0421 Effective date: 19820809 |
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